Total serum angiotensin converting enzyme activity in rats and dogs after enalapril maleate (MK-421).

A centrifugal gel filtration separation of serum angiotensin converting enzyme (ACE) from a potent stable inhibitor is described. This, together with a 20 hr assay incubation of very dilute enzyme, permitted the assessment of the effects of enalapril maleate treatment on total serum ACE in rats and dogs. Total serum ACE increased in both species after 1 or 2 weeks at 10 mg/kg/day. Serum ACE in rats was more than doubled; whereas the increase was modest in dogs (48 +/- 9% minimum). The effect of the drug on serum ACE combined with inherent variability of ACE precluded use of serum ACE activity as an accurate measure of inhibitor concentration in animals receiving enalapril maleate.